U.S. patent application number 14/776761 was filed with the patent office on 2016-01-14 for photonic needle with optimal bevel angle.
This patent application is currently assigned to Koninklijke Philips N.V.. The applicant listed for this patent is KONINKLIJKE PHILIPS N.V.. Invention is credited to WALTHERUS CORNELIS JOZEF BIERHOFF, TORRE MICHELLE BYDLON, BERNARDUS HENDRIKUS WILHELMUS HENDRIKS, GERHARDUS WILHELMUS LUCASSEN, CHRISTIAN REICH, MARJOLEIN VAN DER VOORT, JOHANNES ANTONIUS VAN ROOIJ, STEPHAN VOSS, Klaas Cornelis Jan WIJBRANS, AXEL WINKEL.
Application Number | 20160007841 14/776761 |
Document ID | / |
Family ID | 51657657 |
Filed Date | 2016-01-14 |
United States Patent
Application |
20160007841 |
Kind Code |
A1 |
WIJBRANS; Klaas Cornelis Jan ;
et al. |
January 14, 2016 |
PHOTONIC NEEDLE WITH OPTIMAL BEVEL ANGLE
Abstract
The present invention relates to a medical needle which
comprises an elongate tube and at least one optical fiber, e.g. two
fibers, arranged within the elongate tube, for making optical
measurements at the distal end of the needle. The optical fibers(s)
has a beveled distal end surface, wherein a plane touching the
beveled distal end surface and a longitudinal extension axis of the
optical fiber forms a bevel angle which is 30.degree.-35.degree..
Such needle is advantageous for providing a medical needle which is
reliable and long term stable, can be manufactured in low cost
using known optical fiber materials, thus allowing it to form part
of disposable medical kits. Still, the bevel angle of
30.degree.-35.degree. provides a needle which is easy to insert and
which provides a low tendency to cause tissue sticking. Especially,
the elongate tube and the optical fiber end(s) have the same
beveled angle within the range 30.degree.-35.degree., thus allowing
a smooth front surface of the needle.
Inventors: |
WIJBRANS; Klaas Cornelis Jan;
(RIJEN, NL) ; LUCASSEN; GERHARDUS WILHELMUS;
(EINDHOVEN, NL) ; HENDRIKS; BERNARDUS HENDRIKUS
WILHELMUS; (EINDHOVEN, NL) ; REICH; CHRISTIAN;
(EINDHOVEN, NL) ; VAN ROOIJ; JOHANNES ANTONIUS;
(BEST, NL) ; BIERHOFF; WALTHERUS CORNELIS JOZEF;
(VELDHOVEN, NL) ; VAN DER VOORT; MARJOLEIN;
(VALKENSWAARD, NL) ; WINKEL; AXEL; (ZAPEL-HOF,
DE) ; VOSS; STEPHAN; (SCHWERIN, DE) ; BYDLON;
TORRE MICHELLE; (EINDHOVEN, NL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KONINKLIJKE PHILIPS N.V. |
Eindhoven |
|
NL |
|
|
Assignee: |
Koninklijke Philips N.V.
|
Family ID: |
51657657 |
Appl. No.: |
14/776761 |
Filed: |
April 3, 2014 |
PCT Filed: |
April 3, 2014 |
PCT NO: |
PCT/IB2014/060400 |
371 Date: |
September 15, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61807839 |
Apr 3, 2013 |
|
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|
61836780 |
Jun 19, 2013 |
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Current U.S.
Class: |
600/182 |
Current CPC
Class: |
A61B 5/0084 20130101;
A61B 5/6848 20130101; A61B 1/07 20130101 |
International
Class: |
A61B 1/07 20060101
A61B001/07 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 14, 2014 |
EP |
14155142.4 |
Feb 14, 2014 |
EP |
14155150.7 |
Claims
1. A needle comprising: an elongate tube (T) having a beveled
distal end, and at least one optical fiber (FB1, FB2) arranged
within the elongate tube (T), wherein the optical fiber (FB1, FB2)
has a beveled distal end surface, wherein a plane touching the
beveled distal end surface and a longitudinal extension axis of the
optical fiber (FB1, FB2) forms a bevel angle (B_A) selected within
a bevel angle range of 30.5.degree.-34.5.degree..
2. Needle according to claim 1, wherein a plane touching the
beveled distal end of the elongate tube (T) and a longitudinal
extension axis of the elongate tube (T) forms an angle within said
bevel angle range.
3. Needle according to claim 1, wherein a plane touching the
beveled distal end of the elongate tube (T) and a longitudinal
extension axis of the elongate tube (T) forms an angle which is
equal to or substantially equal to said bevel angle (B_A).
4. Needle according to claim 1, wherein the plane touching the
beveled distal end surface of the optical fiber (FB1, FB2) and the
plane touching the beveled distal end of the elongate tube (T) are
substantially parallel.
5. Needle according to claim 1, wherein the beveled distal end
surface of the at least one optical fiber (FB1, FB2) is plane.
6. Needle according to claim 1, wherein the beveled distal end
surface of the at least one optical fiber (FB1, FB2) is
polished.
7. Needle according to claim 1, comprising a second optical fiber
(FB2) arranged within the elongate tube (T), wherein a plane
touching the beveled distal end surface of the second optical fiber
(FB2) and a longitudinal extension axis of the second optical fiber
(FB2) forms a bevel angle (B_A) selected within said bevel angle
range.
8. Needle according to claim 7, wherein the plane touching the
beveled distal end surface of the first optical fiber (FB1), the
plane touching the beveled distal end surface of second optical
fiber (FB2), and the plane touching the beveled distal end of the
elongate tube (T) are all substantially parallel.
9. Needle according to claim 1, wherein said bevel angle range is
one of 30.degree.-32.degree., 31.degree.-33.degree.,
32.degree.-34.degree., and 33.degree.-35.degree..
10. Needle according to claim 1, wherein said bevel angle range is
one of 31.0.degree.-34.0.degree., 31.5.degree.-33.5.degree., and
32.0.degree.-33.0.degree..
11. Needle according to claim 1, wherein the optical fiber (FB1,
FB2) is made of a material comprising silica.
12. Needle according to claim 11, wherein the optical fiber (FB1,
FB2) is made of undoped fused silica.
13. Needle according to claim 11, wherein the optical fiber (FB1,
FB2) is made of F-doped fused silica.
14. Needle according to claim 1, wherein the at least one optical
fiber (FB1, FB2) is arranged within a stylet insert, wherein the
stylet insert has a bevel at the distal end that has substantially
the same bevel angle as the beveled distal end of the elongate tube
(T), and the stylet insert is arranged within the elongate tube (T)
such that a plane touching the beveled distal end of the elongate
tube (T), and a plane touching the beveled distal end of the stylet
insert are substantially parallel.
15. Interventional medical device comprising the needle of claim
1.
16. Method for optical probing in biological tissue, the method
comprising: providing at least one optical fiber (FB1, FB2) with a
beveled distal end surface, wherein a plane touching the beveled
distal end surface and a longitudinal extension axis of the at
least one optical fiber (FB1, FB2) forms a bevel angle (B_A)
selected within a bevel angle range of 30.5.degree.-34.5.degree.,
and applying light to or receiving light from the biological tissue
through the beveled end surface of the at least one optical fiber
(FB1, FB2).
Description
FIELD OF THE INVENTION
[0001] The invention relates to a photonic or optical needle, i.e.
a needle which incorporates optical fiber(s) or waveguide(s).
Especially, the invention provides a medical needle suitable for
performing optical measurements at the tip of the medical needle in
biological tissue.
BACKGROUND OF THE INVENTION
[0002] In the fields of anaesthesia and pain management the need to
accurately position a medical needle within the body is frequently
encountered. Such needles may be used in the delivery of fluid,
such as an anaesthetic reagent, wherein the position of the
delivery of the fluid is important in achieving an optimal effect
or in avoiding potentially damaging side effects. Likewise, medical
needles that are used to perform a biopsy should be accurately
positioned in order to ensure that the correct tissue sample is
taken from the body.
[0003] Medical photonic needles with optical fibers inside are
known. Such needles allow optical probing of biological tissue,
e.g. for positioning or for other purposes and typically have one
light-supplying fiber and one light-receiving fiber. In alternative
configurations a single fiber performs both light-supplying and
light-receiving functions.
[0004] In the original concept of the photonic needle, a needle
with straight ended fibers at the tip was used as disclosed in
patent application WO2013054254A.
[0005] Medical photonic needles having optical fibers in which the
end surface of the optical fibers are beveled, are also known. See
for example "Epidural needle with embedded optical fibers for
spectroscopic differentiation of tissue: ex vivo feasibility study"
by Desjardins et al, Biomed Opt Express. 2011 Jun. 1; 2(6):
1452-1461. In this publication the beveled surface of the needle
was angled at 20 degrees with respect to the needle axis. Three
optical fibers were embedded in a cannula with epoxy and polished
so that their distal ends were flush with the beveled surface. Such
a small bevel angle provides a sharp point that facilitates
insertion into a body.
[0006] Medical photonic needles in general however, suffer from a
number of problems.
[0007] The optical performance of medical photonic needles having
both straight-cut and beveled optical fiber(s) is conventionally
calibrated in air by placing a reference optical surface in front
of the light supplying fiber such that light is directed back into
the light receiving fiber. The optical performance is determined on
the basis of the proportion of supplied light that is subsequently
received, and on the basis of the optical properties of the
reference optical surface.
[0008] A problem resulting from the usual in-air calibration is
that the amount of internal reflection of light within the optical
fiber at the fiber tip is dependent upon the refractive index of
the optical medium that is in contact with the fiber tip. Since
this optical medium is air, having a refractive index of unity,
during calibration, the differing refractive index of tissue during
use of the medical needle, means that the in-air calibration data
has limited relevance. In order to resolve this issue is it also
known to calibrate the optical fibers of such medical needles in
for example liquid media having a refractive index that is
closer-matched to that of tissue.
[0009] The present invention seeks to improve the robustness of the
optical calibration of such photonic needles.
SUMMARY OF THE INVENTION
[0010] The present invention relates to optical needles having one
or more optical fibers and arises from the insight that the effects
of internal reflection at the fiber tip are exacerbated at small
bevel angles, thus in optical needles having a sharp tip. As the
bevel angle of such an optical fiber is decreased and the fiber tip
becomes sharper, the proportion of light emitted sideways in a
side-lobe, termed an indirect beam, in relation to that emitted in
a direct, or forward-looking beam, is increased. When an in-air
calibration is performed with such a configuration, much of the
light emitted by an optical fiber having a small bevel angle is
emitted in the indirect beam and may miss the reference optical
surface entirely. However when the same sharp bevel angle optical
fiber is placed in tissue, the proportion of light in the indirect
beam falls significantly owing to the closer match between the
refractive index of the optical fiber and that of the tissue,
thereby rendering the calibration of little relevance. This
degrades the robustness of the calibration procedure and increases
the amount of time needed for calibration due to the need to
integrate low signal levels over time. The lack of robustness has
multiple causes in addition to the mix of direct and internal
reflected light distribution described above. These include the
influence of the fiber buffer material and its thickness on the
color of the reflected light, the insight that minute changes in
bevel angle result in large changes in the ratio between internal
reflected light and direct output light, the inconsistency of the
optical performance of the optical needle due to manufacturing
variations, aging of both the buffer material and the fixating glue
under the buffer material, and the sensitivity to the angle under
which calibration is performed in air.
[0011] In tissue, at a 20.degree. bevel angle as used in a prior
art photonic needle, a rather sharp needle, the light output from
the optical fiber is a mix of indirect reflected light and direct
light into the tissue because in tissue only part of the light will
suffer from total internal reflection. The ratio between indirect
light and direct light in tissue varies significantly with small
changes of the bevel angle, meaning that even if a fixed ratio can
be found because the buffer properties can be kept constant, still
no robustness with the database can be achieved if individual
needles have a slight variation of the bevel angle. As a result, it
is no longer possible to calibrate in air. In addition, due to the
light loss when reflecting on the buffer, a much longer calibration
time will be required to perform the calibration without noise,
which is not practical in the workflow. Finally, unlike the silica
core of a fiber, the material for the buffer and the glue are
organic polymers and thus suffer from changing optical
characteristics due to aging. With a required five year shelf life,
this is of importance for calibration.
[0012] Following the above, it is an object of the invention to
provide a medical needle with improved positioning accuracy. It is
further object to provide a medical needle having a needle tip with
a reduced tendency to stick to the tissue or to trap tissue, and
which is easy to insert in biological tissue. It is a further
object to optimize light coupling for illumination and detection.
It is a further object to provide a medical needle which should be
possible to manufacture in a cost effective way, e.g. as disposable
device. Still, it is a further object to provide a medical needle
which has a reliable function even after a considerable time, e.g.
after storage, in case the needle forms part of a disposable
medical kit.
[0013] A first aspect of the invention provides a needle
comprising: [0014] an elongate tube having a beveled distal end,
and [0015] at least one optical fiber arranged within the elongate
tube, wherein the optical fiber has a beveled distal end surface,
wherein a plane touching the beveled distal end surface and a
longitudinal extension axis of the optical fiber forms a bevel
angle selected within a bevel angle range of
30.degree.-35.degree..
[0016] Such optical needle is advantageous since, in essence, it
has been found that the specified bevel angle within the range of
30.degree.-35.degree. of the optical fiber, and preferably the same
angle for the elongate tube, allows a photonic needle which
combines a number of benefits that are differently affected by the
bevel angle. Such needle is suitable for medical applications,
since it has a low degree of tissue sticking due to the rather
sharp bevel angle, it is reliable due to a low sensitivity to
material changes over time because optical side lobes can be
eliminated which allows high calibration reliability. Finally, the
needle can be manufactured using known low cost optical fiber
types, thereby allowing the needle to be economically attractive to
form part of disposable medical kits.
[0017] The invention is based on the insight of a relation between
the bevel angle of the optical fiber, the refractive index of
tissue and a light beam shape, especially the presence of optical
side lobes, for specific and economically attractive materials.
This insight combined with a number of other criteria, has resulted
in providing a bevel angle of specifically 30.degree.-35.degree. as
providing a needle with a number of combined properties which
provides an especially attractive medical photonic needle.
[0018] A plane touching the beveled distal end of the elongate tube
and a longitudinal extension axis of the elongate tube may form an
angle within said bevel angle range (i.e. 30.degree.-35.degree.). A
plane touching the beveled distal end of the elongate tube and a
longitudinal extension axis of the elongate tube may form an angle
which is equal to or substantially equal to said bevel angle. The
plane touching the beveled distal end surface of the optical fiber
and the plane touching the beveled distal end of the elongate tube
may be substantially parallel. Especially, said two planes may be
coinciding, i.e. the optical fiber end being arranged flush with
the beveled distal end of the elongate tube. The needle may
comprise a second optical fiber arranged within the elongate tube,
wherein a plane touching the beveled distal end surface of the
second optical fiber and a longitudinal extension axis of the
second optical fiber forms a bevel angle (B A) selected within said
bevel angle range (i.e. 30.degree.-35.degree.). Especially, the
bevel angle of both a first and a second optical fibers are
selected to be the same. Especially, the plane touching the beveled
distal end surface of the first optical fiber, the plane touching
the beveled distal end surface of second optical fiber, and the
plane touching the beveled distal end of the elongate tube are all
substantially parallel, such as all these three planes
coinciding.
[0019] The bevel angle range may be one of: 30.degree.-32.degree.,
31.degree.-33.degree., 32.degree.-34.degree., and
33.degree.-35.degree.. Alternatively, the bevel angle range may be
one of: 31.degree.-32.degree., 32.degree.-33.degree.,
33.degree.-34.degree., and 34.degree.-35.degree.. Alternatively,
the bevel angle range may be one of: 30.5.degree.-31.5,
31.5.degree.-32.5.degree., 32.5.degree.-33.5.degree., and
33.5.degree.-35.degree.. More alternatively, the bevel angle range
may be one of: 30.degree.-33.degree., 31.degree.-34.degree.,
32.degree.-35.degree., 30.degree.-34.degree., and
31.degree.-35.degree.. Still more alternatively, the bevel angle
range may be one of: 30.5.degree.-34.5, 31.0.degree.-34.0.degree.,
31.5.degree.-33.5.degree., and 32.0.degree.-33.0.degree..
[0020] In preferred embodiments, the optical fiber is made of a
material comprising silica. Especially, the optical fiber can be
made of undoped fused silica. Alternatively, the optical fiber can
be made of F-doped fused silica, e.g. combined with a hard
cladding. It has been found that an undoped fused silica fiber core
can be used for the optical fiber and still provide the desired
optical properties, thereby providing an attractive material for
low cost manufacturing of a disposable medical needle kit.
[0021] A channel may be formed within the elongate tube, so as to
allow transport of a fluid through the medical needle. Especially,
the channel may have a wall which comprises at least a portion of
the inner bore of the elongate tube, alternatively or additionally
the channel may have a wall which further comprises at least a
portion of the outer bore of a stylet insert, in case of
embodiments in which a stylet insert within the elongate tube is
used. As a still further option, the channel may be formed within a
stylet insert.
[0022] The beveled distal end surface of the at least one optical
fiber may be plane, e.g. such that a smooth plane surface which is
polished.
[0023] The optical fiber end(s) may be coated with a coating
covering the distal end surface of the at least one optical fiber.
Such coating may comprise one of: Teflon.RTM., Delrin.RTM.,
silicon, and a lipophobic coating material. The thickness of a
coating layer formed by such coating material may be such as 0.5-2
.mu.m.
[0024] In preferred embodiments, the distal end surface of the at
least one optical fiber has a slanting or bevel angle equal to or
substantially equal to a slanting or bevel angle of the beveled
distal end of the elongate tube. Especially, the slanting angle of
the distal end surface of the at least one optical fiber is
preferably equal to the slanting angle of the beveled distal end of
the elongate tube, and arranged so as to form a plane coinciding
with the plane touching the beveled distal end of the elongate
tube. Hereby, an especially smooth surface of the medical needle
can be provided, thus preventing sticking of tissue.
[0025] The at least one optical fiber may be arranged within a
stylet insert, wherein the stylet insert has a bevel at the distal
end that has substantially the same bevel angle as the beveled
distal end of the elongate tube, and the stylet insert is arranged
within the elongate tube such that a plane touching the beveled
distal end of the elongate tube, and a plane touching the beveled
distal end of the stylet insert are substantially parallel.
Especially, such embodiment may comprise two or more optical fibers
arranged within the stylet insert. E.g. one optical fiber for
transmitting light, and one optical fiber for receiving reflected
and/or light from the tissue.
[0026] It may be preferred that the elongate tube has a circular
cross section.
[0027] In a second aspect, the invention provides an interventional
device comprising a medical needle according to the first
aspect.
[0028] In a further aspect, the invention provides a medical system
comprising a needle according to the first aspect, and an optical
console system comprising a light source and a light detector, and
being arranged for optical connection to the at least one optical
fiber, so as to allow optical interrogation of the at least one
optical fiber.
[0029] In a still further aspect, the invention provides a method
for optical probing in biological tissue, the method comprising:
[0030] providing at least one optical fiber with a beveled distal
end surface, wherein a plane touching the beveled distal end
surface and a longitudinal extension axis of the at least one
optical fiber forms a bevel angle selected within a bevel angle
range of 30.degree.-35.degree., and [0031] applying light to and/or
receiving light from the biological tissue through the beveled end
surface of the at least one optical fiber.
[0032] It is to be understood that the advantages and embodiments
mentioned for the first aspect apply as well for the further
aspects, and the mentioned embodiments of the first aspect may be
combined in any way with the further aspects.
BRIEF DESCRIPTION OF THE FIGURES
[0033] It is to be understood that the illustrations are merely
sketches, and thus the illustrations of the bevel angles should not
be considered as exact illustrations.
[0034] FIGS. 1a and 1b illustrate a prior art needle examples of
light beams from optical fibers with a straight cut fiber end (FIG.
1a), and an optical fiber with a sharp cutting angle (FIG. 1b).
[0035] FIG. 2 illustrates a needle embodiment with two optical
fibers cut in the same bevel angle as the elongate tube forming the
needle structure, here illustrates with a bevel angle of
32.degree..
[0036] FIGS. 3 and 4 illustrate internal reflection in an optical
fiber with slanting or beveled fiber end, and the use of reflecting
coatings that around the optical fiber cladding at the distal end
of the optical fibers in order to improve light delivery and
collection.
[0037] FIG. 5 illustrates a needle embodiment with a slanting or
bevel angle of 31.degree..
[0038] FIG. 6 illustrates a needle embodiment with a double beveled
front.
[0039] FIG. 7 illustrates a graph showing direct versus indirect
beam from an optical fiber as a function of its bevel angle.
DETAILED DESCRIPTION OF THE INVENTION
[0040] FIG. 1a shows a sketch of a prior art needle with two
optical fibers FB1, FB2 with straight-cleaved fiber ends, and their
respective light cones or beams in air L_A and in tissue L_T which
is seen to be practically identical.
[0041] FIG. 1b shows a similar sketch of another prior art needle
with beveled fiber ends with a bevel angle of 25.degree., i.e. a
sharp needle. Here, resulting from internal reflection at the
buffer BF, light beams from one fiber FB1, FB2 in tissue has two
beams L1_T, L2_T, namely the desired forward beam L1_T and an
undesired side lobe L2_T. The corresponding side lobe for air L2_A
is also shown. As seen, a significant amount of the light in tissue
L2_T is directed to the side of the needle.
[0042] FIG. 2 shows a sketch of a needle embodiment with two
optical fibers FB1, FB2 both with the same bevel angle B_A of
32.degree. as the elongate tube T, e.g. metal tube, where the two
fibers FB1, FB2 are arranged within a suitable cladding material.
It is to be understood that a small deviation between bevel angle
for the fiber ends FB1, FB2 and the elongate tube T end may be
acceptable within normal production tolerances, such as e.g.
+/-1.degree.. However, in principle, to avoid tissue sticking, it
is desirable to have a front surface of the needle which is as
smooth as possible. To obtain this, the optical fibers FB1, FB2 are
preferably cut with the same bevel angle as the elongate tube
T.
[0043] FIG. 3 serves to illustrate light coupling for slanted or
beveled optical fiber ends. Slanted fiber ends serve to prevent
pockets that could cause tissue sticking. However, light output
coupling with straight cut fibers is found to be more efficient
compared to the light coupling with slanted fiber ends. Internal
reflections at the slanted fiber interface cause light losses
through the cladding CL and buffer BF. FIG. 3 illustrates step
index fiber with core CR and cladding light is internally reflected
for rays with an angle .theta. that is less than
(90.degree.-.theta..sub.c), where .theta..sub.c is the critical
angle at which the rays still undergo total internal reflection at
the core cladding interface. Light coupling into or outwards from
the fiber occurs for rays with angles .theta. less than
.theta..sub.m. Internal reflection at a slanted fiber interface
towards cladding CL and buffer BF causes reduced light output
coupling for illumination and in coupling for detection since the
angle .theta., for these rays will be .theta. is greater than
(90.degree.-.theta..sub.c) and do not undergo total reflection but
is transmitted to the buffer BF and can be absorbed and scattered
by the buffer material.
[0044] FIG. 4 illustrates the use of reflecting coatings BF_R that
surround the optical fiber cladding CL at the distal end of the
optical fibers in order to improve light delivery and collection.
Such a reflective coating BF_R may be incorporated in a stylet
which retains the optical fibers, or at the inside of the needle or
cannula. Alternatively, a reflecting coating BF_R may be employed
with polished pocket walls that are filled with index matching
optically transparent material.
[0045] FIG. 5 illustrates a needle embodiment with an elongate tube
T and two optical fibers FB1, FB2 which all have one common bevel
angle B_A of 31.degree., and wherein the optical fiber ends may be
polished to form a specially smooth surface.
[0046] FIG. 6 illustrates a needle with a double beveled distal and
of B_A of 33.5.degree.. As seen, one optical fiber FB 1 is
positioned with its distal end flush with a first beveled part,
whereas the second optical fiber FB2 is positioned with its distal
end flush with a second beveled part. In the illustrated
embodiment, the first and second beveled parts are symmetrical,
i.e. both having the same bevel angle B_A, thereby forming a front
of the needle with a 67.degree. angle.
[0047] FIG. 7 shows a graph of a levels of a direct beam D_B and an
indirect beam I_B for a silica optical fiber with NA=0.28, and with
bevel angle B_A. As seen, for small bevel angles B_A_1, i.e. sharp
needles, a small change in bevel angle B_A results in a large
change in ratio between direct and indirect light. Thus, this bevel
angle range B_A_1, especially below some 23.degree., light output
will depend highly on even small production tolerances. By using a
bevel angle B_A of above 28.degree., almost all of the light in
tissue will be in the direct beam, meaning that it is not
influenced by the buffer or glue around the optical fiber. In
addition, above 30.degree., the needle is robust for variation of
the bevel angle B_A, meaning that manufacturing tolerances will not
affect the light output in tissue. Combined with the silica core of
the fiber and a glass-on-glass connector at a disposable product,
this results in a disposable product where the optical
characteristics are robust for manufacturing tolerances and for
aging during the shelve life because only silica is involved in the
optical path. Below 35.degree. the fiber and needle has been found
to be still sharp enough to allow easy insertion in relevant
biological tissue, and still it will provide a low tissue sticking
tendency. Thus, the inventive bevel angle range is
30.degree.-35.degree., indicated by the dashed lines.
[0048] To summarize, the invention provides a medical needle which
comprises an elongate tube and at least one optical fiber, e.g. two
fibers, arranged within the elongate tube, for making optical
measurements at the distal end of the needle. The optical fibers(s)
has a beveled distal end surface, wherein a plane touching the
beveled distal end surface and a longitudinal extension axis of the
optical fiber forms a bevel angle which is 30.degree.-35.degree..
Such needle is advantageous for providing a medical needle which is
reliable and long term stable, can be manufactured in low cost
using known optical fiber materials, thus allowing it to form part
of disposable medical kits. Still, the bevel angle of
30.degree.-35.degree. provides a needle which is easy to insert and
which provides a low tendency to cause tissue sticking. Especially,
the elongate tube and the optical fiber end(s) have the same
beveled angle within the range 30.degree.-35.degree., thus allowing
a smooth front surface of the needle.
[0049] While the invention has been illustrated and described in
detail in the drawings and foregoing description, such illustration
and description are to be considered illustrative or exemplary and
not restrictive; the invention is not limited to the disclosed
embodiments. Other variations to the disclosed embodiments can be
understood and effected by those skilled in the art in practicing
the claimed invention, from a study of the drawings, the
disclosure, and the appended claims. In the claims, the word
"comprising" does not exclude other elements or steps, and the
indefinite article "a" or "an" does not exclude a plurality. Any
reference signs in the claims should not be construed as limiting
the scope.
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